1. Field
This patent specification describes a data communication apparatus, and more particularly a data communication apparatus capable of functioning as an ID tag and an ID-tag read-write device in a relatively compact structure.
2. Discussion
An electric identification tag has come into widespread use for identification of materials such as products in shops, for example, since it is smaller and less expensive and can contains an overwhelming amount of information in comparison with a barcode system. For example, in a second-hand car dealer, an identification tag (hereinafter referred to as an ID tag) is attached to each of cars for sale there. Each one of the ID tags attached to the cars in the shop has a memory in which various kinds of detailed information of the car are stored. All the information can be read wirelessly with a special tool called an ID-tag read-write device. With this system, a buyer who is interested in buying a specific car can read various kinds of detailed information about the car, such as its detailed technical specification and history, for example, only by bringing the ID-tag read-write device close to the ID tag of that specific car.
With an increasing use of such ID tags, the ID-tag read-write device has been combined with the function of the ID tag so that the ID-tag read-write device can also be used as an ID tag.
A background ID-tag read-write device that serves as the ID tag as well as the ID-tag read-write device includes a wireless communicator 1 which includes a passive communicator 2 and an active communicator 3, as shown in FIG. 1. The passive communicator 2 serves as an ID tag to receive a command signal sent from an external apparatus and to return a response signal in response to the command signal. The active communicator 3 serves as an ID-tag read-write device to send a command signal to other apparatuses and to receive response signals from other apparatuses.
The passive communicator 2 is configured to receive signals of a sleep request and a sleep-termination request in addition to the read and write command signals sent from external apparatuses in order to prevent radio interferences caused by other ID tags and ID-tag read-write devices existing together in a wireless communications area. The passive communicator 2 falls into sleep upon receiving a sleep request signal and then it does not respond to the read and write command signals sent from external apparatuses. For example, when a plurality of passive communicators 2 are existing together in a wireless communications area, the plurality of passive communicators 2 except for a specific one are all set to a sleep mode so that the radio interferences caused by other passive communicators 2 can be prevented.
The passive communicator 2 includes a status holder 4 which holds a status of the sleep mode so that the passive communicator 2 is held in the sleep mode until the passive communicator 2 receives the sleep-termination request signal and terminates the sleep mode.
The active communicator 3 is configured to transmit signals of a sleep request and a sleep-termination request to external apparatuses, in addition to the read and write request signals, and to receive response signals from the external apparatuses in response to these sleep and sleep-termination request signals. That is, the active communicator 3 causes a counterpart of the communications to fall into sleep by transmitting the sleep request signal, and to terminate the sleep by transmitting the sleep-termination request signal. Further, before sending any request signals to external apparatuses, the active communicator 3 reads the status of the sleep mode stored in the status holder 4 of the passive communicator 2 and accordingly determines whether or not the passive communicator 2 is in the sleep mode. When the passive communicator 2 is determined as in the sleep mode, the active communicator 3 disables an output of the request signals. Thus, interferences among the request signals to each other can be prevented in a case where a plurality of active communicator 3 are existing together in a same wireless communications area.